1. Field of the Invention
The present invention relates to an apparatus and method for optically determining a range in which a foreign substance attached to a surface of an object, such as dirt, dust, an oil film, a fingerprint, a scratch, flaws, or the like, exists.
2. Description of the Related Art
In recent years, in the field of recording mediums, such as optical discs, magnetic discs, magnetic tapes, etc., in the field of color filters for a liquid crystal display and organic EL display, and in the field of electronic devices, such as semiconductor integrated circuit, or the like, the size of a component incorporated in a product has been reduced to a very small size. As already known in the above fields, along with a significant reduction in the component size, a foreign substance, such as dirt, dust, scratches, etc., attached to an electronic device, which did not cause a significant problem before, brings about a greater adverse influence on the production yield and performance during operation of the electronic device. Thus, an apparatus and method for detecting a foreign substance with high accuracy has heightened in demand. Conventionally, various proposals have been made for such an apparatus and method. One known example of such is a foreign substance detection apparatus disclosed in Japanese Laid-Open Publication No. 6-223384.
FIG. 15 shows a structure of a conventional foreign substance detection apparatus 1500 for use with an optical disc. The foreign substance detection apparatus 1500 includes: a light source 91; an objective lens 92; a quarter waveplate 94; a polarized beam splitter 95; a light receiving element 96; an I-V conversion section 97; and a sum signal generation circuit 98. The light source 91 is, for example, a semiconductor laser. The light receiving element 96 is separated into a first light receiving element 96A and a second light receiving element 96B. The I-V conversion section 97 includes a first I-V conversion circuit 97A and a second I-V conversion circuit 97B.
Next, an operation of the foreign substance detection apparatus 1500 for detecting a foreign substance which is present on an optical disc 93 is described.
The light source 91 emits a light beam toward the optical disc 93. The emitted light beam passes through the polarized beam splitter 95 and the quarter waveplate 94. Then, the light beam is converged by the objective lens 92 on the surface of the optical disc 93 so as to form a light spot thereon. The light beam reflected by the surface of the optical disc 93 passes through the objective lens 92 and the quarter waveplate 94 again, whereby the phase of the light beam is changed. The light beam with the changed phase is reflected by the polarized beam splitter 95 so as to enter the first light receiving element 96A and the second light receiving element 96B. The first light receiving element 96A and the second light receiving element 96B respectively generate a first electric current signal IA and a second electric current signal IB, each of which indicates the quantity of the received light beam. The first electric current signal IA and the second electric current signal IB are transmitted to the first I-V conversion circuit 97A and the second I-V conversion circuit 97B, respectively.
The first I-V conversion circuit 97A and the second I-V conversion circuit 97B convert the respective first electric current signal IA and the second electric current signal IB into a first voltage signal VA and a second voltage signal VB, respectively. The first voltage signal VA and the second voltage signal VB are transmitted to the sum signal generation circuit 98.
The sum signal generation circuit 98 sums up the first voltage signal VA and the second voltage signal VB to generate a sum voltage signal VA+VB. The sum signal generation circuit 98 compares the generated sum voltage signal VA+VB with a reference voltage signal Vref. The reference voltage signal Vref is a voltage signal which indicates the quantity of light calculated from the theoretical reflectance of the optical disc 93 on which no foreign substance is attached.
If the relationship between the reference voltage signal Vref and the sum voltage signal VA+VB is Vref less than VA+VB or Vref greater than VA+VB, the foreign substance detection apparatus 1500 determines that there is a foreign substance present. If the relationship between the reference voltage signal Vref and the sum voltage signal VA+VB is Vref=VA+VB, the foreign substance detection apparatus 1500 determines that there is no foreign substance present.
The foreign substance detection apparatus 1500 has two light receiving elements (the first light receiving element 96A and the second light receiving element 96B), but may have a single light receiving element.
The above described foreign substance detection apparatus 1500 mainly has the two problems (1) and (2) described below.
(1) In the case where the difference between the reflectance of an object (object to be examined) and that of a foreign substance is small, the foreign substance on the object sometimes cannot be accurately detected. Such applies especially to the case of a foreign substance, such as an oil film, a fingerprint, or the like. In this case, a large difference does not occur between the quantity of light reflected by a portion of the object on which the foreign substance exists and the quantity of light reflected by a portion of the object on which the foreign substance does not exist (i.e., a large difference does not occur between the sum voltage signal obtained from the quantity of light reflected by a portion of the object on which the foreign substance exists and the reference voltage signal obtained from the quantity of light reflected by a portion of the object on which the foreign substance does not exist). Accordingly, it is impossible to accurately detect the foreign substance.
Thus, in order to accurately detect such a foreign substance, it is necessary to stabilize the sum voltage signal with high accuracy. However, under a normal environment for using such a detection apparatus, the quantity of light readily varies due to a variation with time, and a variation due to temperature of a light source, a light receiving element, a signal processing circuit, or the like, or due to dust attached to an optical lens, a light receiving element, or the like. Thus, it is difficult to stabilize the sum voltage signal which is generated in a subsequent component. From experimentation conducted by the present inventors, it was confirmed that the sum voltage signal can vary by about 50% under a normal environment.
The sum voltage signal can be stabilized to some extent by using the foreign substance detection apparatus in a clean room, by incorporating a high-precision, complicated control apparatus, by periodically performing maintenance activities, or the like. However, in such cases, the cost efficiency is decreased.
(2) In the conventional foreign substance detection apparatus 1500, the reference voltage signal Vref used for determining the presence/absence of a foreign substance is a fixed voltage signal which indicates, for example, the quantity of light calculated from the theoretical reflectance of an object on which no foreign substance is attached. However, as described above, under an actual environment for using the detection apparatus, the quantity of light reflected by the surface of the object readily varies. Accordingly, the quantity of light reflected by a portion of the object on which no foreign substance is attached, which is measured under the normal environment, is sometimes different from the quantity of light calculated from the theoretical reflectance of the object. As a result, accuracy in detection of a foreign substance decreases.
According to one aspect of the present invention, an apparatus for determining an existence range of a foreign substance which is present on a surface of an object, includes: an optical system including a light source for emitting a light beam onto the surface of the object; a movement section for relatively moving the object with respect to the light beam; a light detection section for detecting a light quantity of the light beam reflected by the surface of the object to generate a light detection signal which indicates the light quantity, the light detection section including a first light detection section for generating a first light detection signal and a second light detection section for generating a second light detection signal; a difference signal generation section for generating a difference signal which indicates a difference between the first light detection signal and the second light detection signal; a perimeter signal generation section for comparing the difference signal with a reference value to generate a perimeter signal which indicates a perimeter of the foreign substance; and a foreign substance determination section for determining an existence range of the foreign substance using the perimeter signal.
In one embodiment of the present invention, the first light detection section and the second light detection section are arranged along the moving direction in this order.
In another embodiment of the present invention, the reference value varies according to an average value of the light quantity of the light beam reflected by the surface of the object on which the foreign substance is not attached.
In still another embodiment of the present invention, the optical system further includes a converging section for converging the light beam on the surface of the object; and the converging section is arranged such that the converged light beam has a wavefront aberration.
In still another embodiment of the present invention, the light beam is monochromic light; and a standard deviation of the wavefront aberration is 0.07 or more times a wavelength of the monochromic light.
In still another embodiment of the present invention, the apparatus further includes a vibration section for vibrating the converging section along a direction parallel to the surface of the object.
In still another embodiment of the present invention, the movement section reciprocates the light beam along a direction parallel to the surface of the object.
In still another embodiment of the present invention, the apparatus further includes a rotation section for rotating the object.
In still another embodiment of the present invention, the movement section oscillates the light beam in a direction perpendicular to the rotation direction of the object.
In still another embodiment of the present invention, the movement section reciprocates the object along a direction perpendicular to the emission direction of the light beam.
According to another aspect of the present invention, a method for determining an existence range of a foreign substance which is present on a surface of an object, includes steps of: emitting a light beam onto the surface of the object; relatively moving the object with respect to the light beam; detecting a light quantity of the light beam reflected by the surface of the object using a light detection section, to generate a light detection signal which indicates the light quantity, the light detection section including a first light detection section for generating a first light detection signal and a second light detection section for generating a second light detection signal; generating a difference signal which indicates a difference between the first light detection signal and the second light detection signal; comparing the difference signal with a reference value to generate a perimeter signal which indicates a perimeter of the foreign substance; and determining an existence range of the foreign substance using the perimeter signal.
In one embodiment of the present invention, the first light detection section and the second light detection section are arranged along the moving direction in this order.
In another embodiment of the present invention, the reference value varies according to an average value of the light quantity of the light beam reflected by the surface of the object on which the foreign substance is not attached.
In still another embodiment of the present invention, the method further includes a step of converging the light beam on the surface of the object, wherein the light beam converged on the surface of the object has a wavefront aberration.
In still another embodiment of the present invention, the light beam is monochromic light; and a standard deviation of the wavefront aberration is 0.07 or more times a wavelength of the monochromic light.
In still another embodiment of the present invention, the step of converging the light beam includes a step of vibrating the light beam over the surface of the object.
In still another embodiment of the present invention, the moving step includes a step of reciprocating the light beam along a direction parallel to the surface of the object.
In still another embodiment of the present invention, the moving step includes a step of rotating the object.
In still another embodiment of the present invention, the moving step includes a step of oscillating the light beam in a direction perpendicular to the rotation direction of the object.
In still another embodiment of the present invention, the moving step includes a step of reciprocating the object along a direction perpendicular to the emission direction of the light beam.
According to still another aspect of the present invention, an apparatus for determining an existence range of a foreign substance which is present on a surface of an object, includes: an optical system including a light source for emitting a light beam onto the surface of the object: a movement section for relatively moving the object with respect to the light beam; a light detection section for detecting a light quantity of the light beam reflected by the surface of the object to generate a light detection signal which indicates the light quantity; an average value calculation section for calculating an average value of the light detection signal; a reference value calculation section for calculating a reference value using a function where the average value is a variable; a comparison signal generation section for comparing the light detection signal with the reference value to generate a comparison signal which indicates presence/absence of the foreign substance; and a foreign substance determination section for determining an existence range of the foreign substance using the comparison signal.
In one embodiment of the present invention, the average value is calculated by the average value calculation section by: obtaining an average value by averaging all values of the light detection signal which indicates the light quantity of the light beam reflected from the surface of the object on which the foreign substance is not attached; and averaging the values of the light detection signal which do not exceed a standard deviation of the obtained average value.
In another embodiment of the present invention, the reference value includes a first reference value X1 and a second reference value X2; the first reference value X1 is used for detecting a foreign substance whose reflectance nvar is larger than a reflectance nob of the object (nob less than nvar); and the second reference value X2 is used for detecting a foreign substance whose reflectance nvar is smaller than the reflectance nob of the object (nob greater than nvar).
In still another embodiment of the present invention, the first reference value X1 and the second reference value X2 are calculated based on an arithmetic operation formula selected from a group consisting of following arithmetic operation formulas:
X1=Xavxc2x7(1+xcex21), X2=Xavxc2x7(1xe2x88x92xcex11);
X1=Xav/(1xe2x88x92xcex12), X2=Xav/(1+xcex22); and
xe2x80x83X1=Xav+xcex23, X2=Xavxe2x88x92xcex13,
where Xav denotes the average value; xcex11, xcex12, xcex13, xcex21, xcex22, xcex23 greater than 0; and xcex11, xcex12, xcex13, xcex21, xcex22, xcex23 are constants.
In still another embodiment of the present invention, the movement section reciprocates the light beam along a direction parallel to the surface of the object.
In still another embodiment of the present invention, the apparatus further includes a rotation section for rotating the object.
In still another embodiment of the present invention, the movement section oscillates the light beam in a direction perpendicular to the rotation direction of the object.
In still another embodiment of the present invention, the movement section reciprocates the object along a direction perpendicular to the emission direction of the light beam.
According to still another aspect of the present invention, a method for determining an existence range of a foreign substance which is present on a surface of an object, includes steps of: emitting a light beam onto the surface of the object; relatively moving the object with respect to the light beam; detecting a light quantity of the light beam reflected by the surface of the object to generate a light detection signal which indicates the light quantity; calculating an average value of the light detection signal; calculating a reference value using a function where the average value is a variable; comparing the light detection signal with the reference value to generate a comparison signal which indicates presence/absence of the foreign substance; and determining an existence range of the foreign substance using the comparison signal.
In one embodiment of the present invention, the step of calculating the average value includes: obtaining an average value by averaging all values of the light detection signal which indicates the light quantity of the light beam reflected from the surface of the object on which the foreign substance is not attached; and averaging the values of the light detection signal which do not exceed a standard deviation of the obtained average value.
In another embodiment of the present invention, the reference value includes a first reference value X1 and a second reference value X2; the first reference value X1 is used for detecting a foreign substance whose reflectance nvar is larger than a reflectance nob of the object (nob less than nvar); and the second reference value X2 is used for detecting a foreign substance whose reflectance nvar is smaller than the reflectance nob of the object (nob greater than nvar).
In still another embodiment of the present invention, the step of calculating the reference value includes a step of obtaining the first reference value X1 and the second reference value X2 based on an arithmetic operation formula selected from a group consisting of following arithmetic operation formulas:
X1=Xavxc2x7(1+xcex21), X2=Xavxc2x7(1xe2x88x92xcex11);
X1=Xav/(1xe2x88x92xcex12), X2=Xav/(1+xcex22); and
X1=Xav+xcex23, X2=Xavxe2x88x92xcex13,
where Xav denotes the average value; xcex11, xcex12, xcex13, xcex21, xcex22, xcex23 greater than 0; and xcex11, xcex12, xcex13, xcex21, xcex22, xcex23 are constants.
In still another embodiment of the present invention, the moving step includes a step of reciprocating the light beam along a direction parallel to the surface of the object.
In still another embodiment of the present invention, the moving step includes a step of rotating the object.
In still another embodiment of the present invention, the moving step includes a step of oscillating the light beam in a direction perpendicular to the rotation direction of the object.
In still another embodiment of the present invention, the moving step includes a step of reciprocating the object along a direction perpendicular to the emission direction of the light beam.
Thus, the invention described herein makes possible the advantages of (i) providing an apparatus and method capable of detecting, with high accuracy, a foreign substance on an object in the case where a difference between the reflectance of the object and that of the foreign substance is small; and (ii) providing an apparatus and method capable of detecting a foreign substance with high accuracy, and capable of detecting the range on an object in which a foreign substance exists regardless of a variation in the quantity of light reflected by the object which is caused according to the environment for using the apparatus.
These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.